The invention relates to an electrostatic apparatus for controlling the volume rate of flow of liquid.
The conveyance of liquid is generally accomplished by either pressurizing or by suction. A base volume rate of flow of a liquid being conveyed is adjusted by setting the pressure for conveyance and/or using a metering device such as a metering orifice.
A mechanical flow control device such as a valve or an injector which is operated electrically, hydraulically or pneumatically is used when a minute regulation of the flow rate around the preset basic flow rate is intended. There is a limit to the responsiveness of such a flow rate control device due to the inclusion of a moving mechanism. In the case of the flow control device being of the on-off functioning type such as a solenoid valve, the operation of the device tends to cause pulsation in the liquid flow as a factor unfavorably affecting the precision in the control. Accordingly a practical control of the flow rate encounters a technical difficulty when it is necessary to accomplish the control with very high precision.
A fuel supply system in automotive internal combustion engines is a typical example of liquid conveyance systems which require a high precision control of the flow rate. In this fuel supply system, metering of a liquid fuel is accomplished by means of either a carburetor or a fuel injector in order to prepare a combustible air-fuel mixture having a desired air/fuel ratio. In recent years, there is a strong and growing demand for a technique for very precisely controlling the air/fuel ratio in the field of automotive engines since such a technique is almost a requisite for the success of recently developed methods for reducing the emission of pollutants and/or improving the fuel economy. Principally this demand can be satisfied by an electronic air/fuel ratio control system which performs a feedback control of the fuel supply rate based on the concentration of a specific component of the exhaust gas. This air/fuel ratio control system usually includes an electromagnetic valve (which has the aforementioned disadvantages) as a fuel supply rate regulation means, so that the performance of this control system in practical application is not yet fully satisfactory. At present, however, there is no different type of flow control device which serves as a superior substitute for the electromagnetic valve in the feedback air/fuel ratio control system.